| Message ID | 20190415155452.5115-2-kwolf@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | qcow2: Preallocation fixes | expand |
On 4/15/19 10:54 AM, Kevin Wolf wrote: > Limiting the allocation to INT_MAX bytes isn't particularly clever > because it means that the final cluster will be a partial cluster which > will be completed through a COW operation. This results in unnecessary > data read and write requests which lead to an unwanted non-sparse > filesystem block for metadata preallocation. > > Align the maximum allocation size down to the cluster size to avoid this > situation. > > Cc: qemu-stable@nongnu.org > Signed-off-by: Kevin Wolf <kwolf@redhat.com> > --- > block/qcow2.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/block/qcow2.c b/block/qcow2.c index d507ee0686..c8400e9712 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2723,6 +2723,7 @@ static int qcow2_set_up_encryption(BlockDriverState *bs, static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset, uint64_t new_length) { + BDRVQcow2State *s = bs->opaque; uint64_t bytes; uint64_t host_offset = 0; unsigned int cur_bytes; @@ -2733,7 +2734,7 @@ static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset, bytes = new_length - offset; while (bytes) { - cur_bytes = MIN(bytes, INT_MAX); + cur_bytes = MIN(bytes, QEMU_ALIGN_DOWN(INT_MAX, s->cluster_size)); ret = qcow2_alloc_cluster_offset(bs, offset, &cur_bytes, &host_offset, &meta); if (ret < 0) {
Limiting the allocation to INT_MAX bytes isn't particularly clever because it means that the final cluster will be a partial cluster which will be completed through a COW operation. This results in unnecessary data read and write requests which lead to an unwanted non-sparse filesystem block for metadata preallocation. Align the maximum allocation size down to the cluster size to avoid this situation. Cc: qemu-stable@nongnu.org Signed-off-by: Kevin Wolf <kwolf@redhat.com> --- block/qcow2.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)